Uranium alloys



Unie

as represented by the United States Atomic Energy Commission No Drawing.pplication July 2, 1946 Serial No. 681,120

7 Claims. or. 75-13:!

This invention relates to new ternary alloys of uranium.

An object of the invention is to provide a composition predominantly ofuranium metal having a resistance to corrosion substantially greaterthan uranium metal.

Another object is to provide a corrosion-resistant uranium alloy.

Another object is to provide a metallic composition containing uraniumhaving a resistance to corrosion substantially greater than uraniummetal and a neutron-capture cross section predominantly determined bythe uranium content.

Another object is to improve the resistance to corrosion of uraniummetal by admixture of one or more other elements of small competitiveneutron absorption.

When uranium is to be subject to irradiation by thermal neutrons forpurposes involving atomic disintegration the extent to which anyimpurity in the uranium metal can be tolerated is determined by thecompetitive neutron absorption (referred to as C.A.) of that impurity.The CA. of an element contained in uranium depends on the capturecross-section (for thermal neutrons) of its atom compared to that of auranium atom and upon the proportion or actualconcentration of atomspresent. Thus the CA. due to an amount of impurity or adulterantexpressed as a proportion by weight can be calculated.

In co-pending application Serial No. 678,887, filed June 24, 1946, andnow abandoned, I have described new alloys containing uranium andmolybdenum, such alloys primarily having greater corrosion resistancethan uranium itself.

According to the present invention I provide a new ternary alloy ofwhich the major proportion consists of uranium, and the minor proportionof molybdenum and silicon. I have found it possible to achieve a markedimprovement in corrosion resistance by employing only a small proportionof molybdenum and of silicon, e.g. of the order of 1 percent of each. Ihave not observed any marked further improvement in corrosion resistanceby increasing the proportions of molybdenum and silicon to highervalues, but it is to be understood that the present invention does notexclude such higher proportions, although in the case of alloycompositions containing considerably greater proportions of molybdenumand silicon, e.g. more'than percent ofeach, difiiculty may beexperienced in the manufacture of the alloys and the competitiveabsorption becomes inconveniently large. Accordingly the preferredalloys contain between 0.1% and 5% molybdenum and between 0.1% and 5%silicon, the balance being substantially uranium. I believe that anyimpurities conventionally present in uranium, molybdenum or silicon donot militate against the corrosionresistance which is characteristic ofthe preferred alloys of the present invention, and it is to beunderstood that the terms uranium, molybdenum and silicon as used hereindenote those metals in the degree of purity customarily available.

Molybdenum has a neutron capture cross-section, such States atent thatits competitive absorption is about 1% when it is uniformly admixed withuranium in the proportion of 1% Similarly silicon has a competitiveabsorption of about 1% when it is present in the proportion of 3.6%.Thus molybdenum and silicon each present in the proportion of 1% in auranium alloy introduce a total competitive absorption of about 2.7%.Ina specific alloy referred to hereinafter containing 0.34% molybdenumand 0.57% silicon the competitive absorption due to these two elementsis about 0.5%.

The alloy compositions of the present invention may be manufacturedby'melting suitable proportions of uranium, molybdenum and silicontogether, e.g. in a thoria crucible at 1150-l400 C., out of contact withair, for example under a flux covering or in vacuo.

If desired, these compositions may be annealed in order to relievestresses in the alloy. The annealing conditions depend primarily on theproportions of molybdenum and silicon in the alloy. With for example0.2-1 percent of each of molybdenum and silicon the annealing may becarried out at 600-500 C. for 8 hours followed by quenching or slowcooling, or at 700-800 C., for 4 hours.

The following is an example of the improvement in thecorrosion-resistant properties of uranium which can be effected byalloying with small amounts of both molybdenum and silicon. An alloycontaining 0.34 percent molybdenum, 0.57 percent silicon and theremainder uranium, obtained by fusion under vacuum in a thoria crucibleat 1300 C., and subsequently annealed at 800 C. for 2 hours and allowedto cool slowly, had a corrosion rate in boiling water of between 0.03and 0.3 mm. per annum and a Brinell hardness of 290-360. For comparison,metals of the same degree of purity being employed, the corrosion ratesof uranium itself, an alloy containing 0.42 percent molybdenum, and anannealed alloy containing 0.77 percent silicon, are respectively 7-16,6-12 and 2.5 mms. per annum. The Brinell hardness was 180-210. Thus, theimprovement in corrosion-resistant properties for the ternary alloys isgreater than would be expected from a knowledge of the two binary alloysinvolved.

In addition, the tensile strength of these alloys is higher in generalthan that of uranium itself, especially when the alloys are annealed.For example, an alloy containing 0.5% silicon, 0.5 molybdenum, thebalance being uranium except principally for 0.07% iron, 0.015% copper,and made by melting suitable proportions of silicon, molybdenum anduranium under an absolute pressure of 10- mms. of mercury, had anultimate stress of 35 tons per square inch, elongation 1%, and reductionin area nil. The same alloy was also annealed at 600 C. for 8 hoursunder an absolute pressure of 10- mms. of mercury and cooled in thefurnace at a rate such that the alloy took 8 hours to cool to C. and 14hours to cool to room temperature. The annealed alloy had an ultimatestress of 44 tons per square inch, elongation 1-2% and reduction in area1-2%. For comparison, the original uranium used for making up thesealloys, either in the form of extruded bar which normally has a highertensile strength than similar material in the ascast condition, or inthe annealed condition after heat treatment at 600 C. for 8 hours andcooling in the furnace, had an ultimate stress of only 25-30 tons persquare inch. The analysis of this uranium was as follows: uranium99.69%, magnesium 0.001%, silicon 0.049%, tin less than 0.001%, iron0.055%, copper 0.060%, calcium less than 0.001%. More highly purifieduranium generally has a higher tensile strength and improved ductility,but even with such material the tensile strength is increased by theaddition of small amounts such as 0.2% to 5% of silicon and molybdenum.

I claim: l. Ternary alloy comprising uranium predominating amount andminor proportions not more than five percent. by weight each of siliconand molybdenum, the,

5. An annealed uranium alloy containing from 0.2 percent to 1 percent ofmolybdenum and from 0.2 percent to 1 percent of silicon, the balanceuranium.

6. Alloy comprising at least 98 percent by weight of uranium and siliconand molybdenum each in amount from 0.1 percent up to one percent byweight.

7. Uranium alloy comprising 0.34 percent molybdenum and 0.57 percentsilicon, the balance uranium.

References Cited in the file of this patent UNITED STATES PATENTS969,064 Kuzel Aug. 30, 1910 1,551,333 Schriiter et al. Aug. 25, 19251,994,805 Kluger Feb. 19, 1935 Hensel et a1 Apr. 16, 1940

1. TENARY ALLOY COMPRISING ARANIUM PREDOMINATING AMOUNT AND MINORPROPORTIONS NOT MORE THAN FIVE PERCENT BY WEIGHT EACH OF SILICON ANDMOLYBDENUM, THE ALLOY HAVING A CVORROSION RESISTANCE GREATER THAN THATOF URANIUM AND A NEUTRON-CAPTURE CROSS-SECTION PREDOMINANTLY DETERMINEDBY THE URENIUM CONTENT.